1. Field of the Invention
This invention relates to gel filled flexible articles and the gels therefor.
Description of the Prior Art
The combination of a silicone rubber container filled with a silicone gel is well known in the art. Such articles are known for use as surgically implantable human breast prostheses, as well as, external breast prostheses. Cronin in U.S. Pat. No. 3,293,663 describes a silicone rubber container filled with a soft silicone gel as an implantable breast prosthesis. Cronin describes a suitable gel as being one disclosed by Nelson in U.S. Pat. No. 3,020,260. The organosiloxane gel disclosed by Nelson is a reaction product of an intimate mixture of a triorganosiloxy endblocked polydiorganosiloxane having a viscosity of 100 to 10,000 cs. (approximately 0.1 to 10 pascal-seconds) at 25.degree. C. and at least 0.174 molar precent of the units are RViSiO where Vi is vinyl and R is methyl or phenyl, and a liquid hydrogensiloxane of the formula EQU HRCH.sub.3 SiO(R.sub.2 SiO).sub.n SiCH.sub.3 RH
where R is methyl or phenyl and n has a value to provide a viscosity of no more than 10,000 cs (approximately 10 pascal-seconds) at 25.degree. C. and a platinum catalyst. These gels have at least one RViSiO unit for each silicon-bonded hydrogen atom. Cronin uses a gel where the ratio of atoms of silicon-bonded hydrogen per gram molecular weight of triorganosiloxy endblocked polydiorganosiloxane is adjusted to about 1.3 and where this gel preferably has a penetration from 30.0 to 20.0 mm. Cronin also suggests that the gel should be one which is inert toward the container. Other references to implantable prostheses include U.S. Pat. Nos. 3,559,214; 3,600,718; 3,665,520; 3,681,787; 3,852,832; and 3,934,274. External breast prostheses using silicone rubber containers and filled with silicone gel are described by Hankin et al. in U.S. Pat. No. 3,896,506 and Hankin in U.S. Pat. No. 3,911,503. These various patents describe methods of manufacture, designs and construction of both implantable and external breast prostheses. They also show the desirability of using silicone rubber containers with a silicone gel filling because of the low reactivity of the body toward the silicone materials and because the silicone materials may be easily cleaned and sterilized by steam or boiling water. Although these references show the desirability of the silicone materials, they do not discuss the problem encountered in using a silicone rubber as the container material and a silicone gel as the filling material. When a silicone gel is in contact with a silicone rubber there is a tendency for components of the gel to exude through the silicone rubber. If the gel filled silicone rubber container is an external breast prosthesis, the exudate will stain the wearer's clothing and be embarrassing. It is, therefore, desirable to reduce or eliminate the exudation, oiling or bleed of the gel components through the silicone rubber container. The prior art silicone gel filled silicone rubber containers have an undesirable amount of oiling or bleed because in order to obtain the desired penetration values for the gel with the appropriate natural simulated characteristics, large amounts of unreacted fluid were included in the gel network. This fluid would bleed through the silicone rubber container walls and thus be a problem as described above. A combination of materials has now been discovered which will provide an article with reduced oiling without departing from the desirable silicone materials.